Tunnel kilns with roof



Feb. 10, 1970 Q CREMER ET AL 3,494,601

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Heinz BEI-RENS United States Patent F 52,24 Inf. c1. F271) 9/26, 9/36, 3/16 U.S. Cl. 263-28 4 Claims ABSTRACT OF THE DISCLOSURE The specification describes tunnel kilns in which, in order to improve atmosphere ow conditions within the kiln, at the upstream end of the ring zone the roof of the kiln is at a higher level.

The tunnel of a tunnel kiln as used in the ceramics industry can generally be divided into a pre-firing zone or length, a firing zone or length and a following cooling length. While in the pre-firing length and in the cooling length there are usually no heating arrangements and the transfer of heat to and from the articles to be fired takes place by means of heat exchangers, for example by means of pipe coils carrying a liquid heat exchanging medium, in the firing length burners operated by fluid fuel, that is to say liquid or gaseous fuel, are provided. It is also possible to heat the ring length electrically.

The present invention is more particularly concerned with tunnel kilns whose ring lengths are heated by means of uid operated burners.

The combustion air required for the burning of the fluid fuel can either be fed to the burners directly or the tunnel kiln can be operated in accordance with the circular or ring kiln principle. In this case the kiln atmosphere is drawn into the tunnel by the tunnel draught at the end at which the trolleys leave the kiln. The kiln atmosphere then passes through the cooling length, the tiring length and finally the pre-firing length or zone from which it is removed by ues. The kiln atmosphere thus moves substantially horizontally along the tunnel from the exit end, that is to say the end at which the goods leave the kiln, to the inlet end. However, even in those cases in which air for combustion is fed directly to the burners there is practically always a horizontal movement of the kiln atmosphere in a direction opposite to the direction of travel of the trolleys from the cooling length through the firing length to the pre-tiring length because it is necessary to prevent products of combustion, that is to say waste gases pervading the cooling length where they would be likely to cause visible or other forms of damage to the goods fired.

The burners red with fluid fuel are generally arranged in the ring length of the tunnel approximately at the same height as to the platforms of the trolleys on which the goods to be fired are stacked. Generally the burners are arranged so as to be transverse in relation to the direction of travel of the trolleys along the tunnel.

The horizontal movement of the tunnel kiln atmosphere from the cooling length and then through the firing length has the consequence that with the above mentioned arrangement of the burners at the height of the platform of the trolleys at the end of the firing length, that is to say adjacent to the last burner or burners, the temperature characteristic of the kiln atmosphere due to the heating effect of the last burner or burners, and therefore also the temperature of the material to be red does not increase in an upmard direction as would be the case with a simple upward movement of the kiln atmosphere, due to the heating eiect, without the superposed horizon- 3,494,601 Patented Feb. 10, 1970 ICC tal flow along the kiln, Thus, owing to this horizontal component of movement which is present in the direction of the tunnel kiln inlet, there is a distortion of the natural thermal upward movement of the kiln atmosphere and therefore of the temperature characteristic or distribution in the direction of tlow of the horizontally moving tunnel kiln atmosphere. Owing to this complex state of affairs the temperature above the burner or burners in question just below the tunnel kiln roof is substantially less than in the region of the burner or burners themselves. It has been found that this is disadvantageous in practice and is potentially likely to impair the quality of the goods tired in the kiln.

As just explained the flow pressure and draught relationship in the burning zone of a tunnel kiln are of complex character: the heated kiln atmosphere tends to rise owing to natural thermal upthrust and this in itself has the tendency to lead to the production of substantially higher temperatures under the roof of the kiln than the level of the carrying surfaces of the trolleys. Measurements show that the boundary layer immediately under the tunnel kiln roof has the highest temperature. On the other hand owing to the chimney draught there is complex intluencing of this tendency for the highest temperature to be immediately under the roof.

One object of the present invention is to prevent this disturbance of the desired temperature characteristic in the part of the kiln heated by the last burner or burners of the ring zone.

A further object of the invention is to prevent this disturbance using simple means.

A further object of the invention is to prevent the disturbance using means which influence the gas flow directly, that is to say by direct liow guiding means rather than by further heating or cooling means,

In accordance with the invention the tunnel roof at the downstream end of the firing length of the kiln is at a higher level than the remaining parts of the firing zone.

At the downstream end of the firing zone the roof can have an upwardly extending recess in the form of an inverted transverse channel.

Fluid burning burners can be arranged under the part of the roof at the higher level.

In order that the invention may be readily understood by those in the art, embodiments of it are described with reference to the attached drawings.

FIG. l is a longitudinal section through a tunnel kiln of conventional construction with diagrammatic representation of the flow of the kiln atmosphere and the gaseous products of combustion rising from the burners.

FIG. 2 is a longitudinal section in accordance with FIG. 1 modied in accordance with the invention.

FIG. 3 is a somewhat modied embodiment of the tunnel in accordance with FIG. 2.

FIG. 4 is a section on the line 3 3 of FIG. 3.

FIG. 5 is a section on the line 3 3 of FIG. 3 in the case of a tunnel kiln with -a vaulted roof.

Referring now to the drawings and more particularly to FIG. l, reference numeral 1 denotes a tunnel kiln shown diagrammatically in section. A, B, and C denote, respectively, the cooling zone or length of the kiln, the tiring length and the pre-firing length of the kiln. The arrow D denotes the direction of travel of trolleys, not shown, in FIG. l.

The horizontally owing kiln atmosphere is denoted by arrow 1 while the arrows directed obliquely upwards denote gaseous products of combustion rising from the burners 3.

In the ease of no horizontal components of movement along the kiln tunnel, the gaseous products of combution will rise substantially vertically. However, they are diverted in the manner shown by the presence of a horizontal flow of the kiln atmosphere as shown, the

result being, as-indicated in FIG. 1, that adjacent to the last burner in front of the cooling zone there will be no temperature characteristic in upward direction which agrees with the temperature characteristic in the remainder of the firing length B. The principal object of the present invention is to avoid this discrepancy as regards. temperature characteristicsy in the downstream end of the firing length or zone.

In accordance with the embodiment of the invention as shown in FIG. 2 the arrows 21r denote the horizontally moving atmosphere travelling along through vthe cooling length of the tunnel. Reference numeral 23 indicates burners in the firing length B. The gaseous products of combustion rising from these burners 23 can in this case move upwards without being disturbed 'along the paths 22. The practically undisturbed upward movement of these gaseous products of combustion is due to the fact that at the downstream end of the firing length or zone of the kiln the kiln roof is Vat a substantially higher level at 24 than at the position 25. In the specific embodiments of the invention shown this part of higher level 24 is due to the provision of a transverse inverted channel-shaped recess in the roof structure. Owing to this higher portion of the roof the horizontally moving kiln atmosphere can move in an upward direction as is indicated by reference numeral 26 so that the horizontal ow is no longer sucient to displace the gaseous products of combustion 22 rising from the burners 23, as is shown in the construction of FIG. l, in an arcuate manner in the direction of the goods inlet end D of the kiln.

FIG. 3 shows an embodiment of the invention in which under the corresponding raised part 34 of the roof 35 there are additional burners 37 above the goods to be iired. These burners, are preferably operated with fluid fuel, that is to say oil or gas which heats the goods to be red from above substantially by radiation.

Reference numeral 32 denotes the burners at the bottom of the kiln while reference numeral 36 denotes the goods on the trolleys 38 which are Imoved through the kiln from left to right in terms of the FIG. 3.

In FIG. 4 reference numeral 34 generally indicates the raised portion of the tunnel kiln roof over the last three burners as is shown in longitudinal section in FIG. 3 and also FIG. 2. Reference numeral 37 indicates the burners arranged under the raised portion of the tunnel roof, while reference numeral 32 denotes those burners which are approximately at the same level as thevcarrying plat. forms of the trolleys. Reference numeral 38 denotes the trolley while reference numeral 36 denotes the goods to be fired.

The embodiment of the invention as shown in FIG. 5 differs from that shown in FIG. 4 only in that the roof of the tunnel kiln is vaulted. The raised part of the tunnel roof over the last three burners of the burning zone is in this case denoted by reference numeral 34a.- The remaining reference numerals correspond to those of FIG. 4.

In the embodiments of the invention as shown in FIGS. 2 through 5 it is assumed that the raised portion of the tunnel kiln roof is over the last three burners in the burning zone B and ends immediately after the last burner. However, this prescription need not be preciselyadhered to and there isV some latitude as regards the number of burners over which the raised portion extends. The necessary length of the raised portion depends onVv the dimensions ofthe tunnelk kiln and from the operational conditions. l

It is not necessary in all cases to cause the raised portion of the roof to end immediately above the last burner. In some cases it may be advantageous to continue the raised portion beyond the last burner. In other cases, on the other hand, it may be appropriate to cause the raised portion of the roof to end before the last burner. In each case, however, the raised portion of the kiln roof must lie in the downstream part of the firing zone, that is to say downstream in relation to the direction of travel of the goods to be fired. It should be in the downstream half of the firing length. The term ring zone or length is used to mean that length of the tunnel kiln which extends from the rst to the last laterally arranged burners at the bottom part of the articles to be red.

' We claim:

1. In a tunnel kiln heated by uid fuel and serving for tiring ceramic articles, having a horizontally extending tunnel, with a roof, in which burner means are placed for maintaininga ring length vor zonel in the tunnel of the kiln, the tiring zone being preceded by a heating-up length and followed by a cooling length, trolleys arranged to move along the kiln tunnel through the heating-up length, the firing length and the cooling length, the kiln atmosphere being arranged to move along the tunnel, in a direction opposite to the direction of travel of the trolleys, from the cooling length into the firing length and thence into the heating-up length, the invention which consists in that the tunnel roof at the downstream end of the firing is at a higher level than in the rest of the firing length.

2. A structure as set forth in claim 1, in which the roof at the downstream end of the firing zone has an upwardly extending recess in the form of an inverted transverse channel.

3. A structure as set forth in claim 1, further comprising uid burning burner means under the part of the roof at a higher level.

4. In a tunnel kiln serving for firing ceramic articles,

the kiln including a horizontally extending tunnel with a roof, said tunnel having in seriatim a heat-up zone, a firing zone, and a cooling zone, and trolleys arranged to move along the kiln tunnel serially through said zones with the kiln atmosphere moving in the opposite direction, the invention which comprises:

burner means positioned longitudinally along the floor of said firing zone for heating said articles as they pass through said zone above said burner means; and a channel shaped recess in the tunnel roof extending from approxi-mately the downstream end of the firing zone to no further than midpoint of said zone for directing the longitudinally moving kiln atmosphere upwardly to permit the heat from said burner means to rise, approximately vertically to heat said articles throughout the tiring zone.

References Cited UNITED STATES PATENTS 832,358 10/ 1906 Bergendal 263-28 1,529,755 3/1925 Stein 263-28 FOREIGN PATENTS 943,511 5/1956 Germany.

OTHER REFERENCES German printed application No. S 42,046, Aug. 30, 1956, Benischte.

IOHN I. CAMBY, Primary Examiner U.S. Cl. X.R. 34-201; 263-7 

